Briefly, the most important application of this invention has to do with a method of making a plug-in fuse assembly like that disclosed in said U.S. Pat. Nos. 3,909,767 and 3,962,782, which preferably comprises a plug-in fuse element including a plate-like body of fuse metal having a pair of laterally spaced terminal blade portions to be received by pressure clip terminals in a mounting panel, current carrying extensions at the inner end portions of the pair of terminal blade-portions and a fuse link portion generally of reduced thickness and very small cross-sectional area interconnecting the current-carrying extensions.
Generally, the method of making such a plug-in fuse assembly disclosed in said U.S. patents comprises providing a blank of fuse metal which is blanked or stamped to provide the pair of laterally spaced terminal blade portions which, when the fuse link portion to be formed therefrom are very fragile, and interconnected by a transverse relatively rigid web. The exposed transverse web interconnecting the pair of terminal blade portions adds rigidity to the blank and securely maintains the relative positions of the pair of terminal blade portions, the current-carrying extensions and the fragile interconnecting link portion of reduced thickness, as a housing or the like is inserted over and secured to th blank. Thus, distortion, breakage or other damage to the blank is effectively prevented during these operations.
The housing is preferably inserted over the blank of fuse metal, preferably by way an of opening at the inwardly facing side of a one piece body of insulating material forming the housing, with the current-carrying extensions and the interconnecting fuse link portion of the blank preferably within the housing and with the pair of terminal blade portions of the blank, which are generally interconnected by the relatively rigid transverse web where the fuse link portion is fragile, extending outwardly from the housing preferably through the opening therein. The blank of fuse metal is suitably secured in the housing as by staking or the like. The housing is thus secured to the blank so that is acts as a rigid insulating body connected between the current-carrying extensions and/or terminal blade portions of the partially enclosed plug-in fuse element. While less desirable, the housing function for this body of insulating material can be eliminated so it acts only as a rigid support and, if desired, a convenient gripping surface for the plug-in fuse element. Where used, the exposed transverse web of fuse metal interconnecting the exposed terminal blade portions of the blank is then blanked or otherwise removed to complete the formation of a housed plug-in fuse element whose exposed pair of terminal blade portions may be insert-into metal sockets or the like of a terminal strip.
For maximum mass production efficiency of the housed plug-in fuse element just described, the blank of fuse metal from which each plug-in fuse element is formed is preferably part of a long strip of fuse metal upon which various blanking operations are performed as the strip moves past various stamping stations. The individual plug-in fuse elements are not completely separated from the strip until just before or after the housing is applied thereto at the end of the strip. The fuse link portions of the plug-in fuse elements are, as previously indicated, preferably of reduced thickness from that of the rest of the fuse-forming elements, and, in the case where the fuse elements are formed from a strip as just described, it is most convenient to provide the strip with a continuous band of reduced thickness extending parallel to the length of the strip, and preferably in the central portion thereof. As disclosed in co-pending application Ser. No. 698,072, filed June 21, 1976, on a Method of Making Miniature Plug-In Fuses of Different Fuse Ratings, plug-in fuse elements of different ratings are formed by varying the locations and/or configurations of the fuse-forming links stamped from the reduced portion of the strip.
One of the cost saving and size reducing aspects of the present method of making plug-in fuses just described is that each plug-in fuse element is a stamping made from a blank or strip of fuse metal, and a completely housed fuse results from merely enclosing the same in an insulating housing, so that the entire fuse assembly is formed of only two parts, and without any soldering operations required to connect a fuse link between the terminal portion of the fuse. However, the metal alloys constituting the fuse metal are readily oxidizable materials, and to insure a continuing low resistance contact between the terminal portions of the plug-in fuse elements are inserted, there should be an appreciable area of good electrical contact between the sockets and the exposed portions of the fuse metal, which is not possible if a thick oxidized film builds up on the surface of the terminal portions of the plug-in fuse element, particularly before it is inserted into the sockets. Oxidization of fuse metals can be prevented by applying a conductive coating over the fuse metal by plating techniques well known in the art. Tin coating is one common method of preventing oxidation of various metals. However, the electroplating of tin upon the exposed terminal-forming portions of the fuse-forming elements described can be a costly procedure because it must be selectively applied so that the fuse-forming link portions of the plug-in fuse elements are not similarly coated, since a tin coating thereon would undesirably modify the blowing characteristics of the fuse. For example, selectively coating the terminal portions of a plug-in fuse element by placing the fuse element in a suitable holder and immersing only the terminal portions thereof in an electro-plating tank would be a relatively costly procedure.